Construction of wooden stairs for residential use is a surprisingly painful process for the builder.
The stairs must obviously traverse a vertical height from one end to the other, however, in most instances, the horizontal run of the stairs is pre-set by an architect while the vertical height may or may not be set: outdoor patio steps, for example, will depend upon the distance from the top of the patio to the ground or landing at the lower end. Thus the builder must construct the steps within an entirely defined boundary.
Since local building codes, the Americans with Disabilities Act and other regulations and rules require that steps be of even height, that is, each step being the same height as the steps above and below it, the builder must then divide the height change into a number of even increments. For example, a height change of 8′3½″ (99.5 inches) would not allow 10 steps of 10 inches each, as one step would be ½ inch short. Rather, the builder would have to calculate some reasonable number of inches per step and number of steps which “works” for the given height and is possible to do. In the given example, cutting 10 steps of 9.95 inches each is probably not possible as most construction measuring devices are denominated in units of ⅛ inch, 1/16 inch, and so on, but not 1/20 (0.05) of an inch. Rounding to the nearest ⅛ inch unit would result in the ½″ deviance mentioned previously, cutting long pieces of wood on-site to within 1/16 of an inch tolerance is difficult at best and would still leave some small deviation. In this case the builder might, after some math headaches, conclude that 8 rather tall steps of 12 7/16″ (12.4375″), would be difficult but at least would be even. However, under the Uniform Building Code at the present time in the US steps must be no more than 8″ in height, thus sending the builder back to the math.
Obviously, this example is constructed to be very annoying to the builder, but the problem is a real one even with simpler numerical requirements.
Once the math problem has been accomplished the builder's problems are NOT over. The builder must then obtain a comparatively expensive piece of wood for the “stringer”, that is, the main support beam of the stairway which runs at a diagonal from lower end to upper end, holding up all of the stairs.
A stringer is a single strong piece of wood, usually a 2×12 or the like, which under many codes must be solid wood, not composite material such as plywood or the like as composites are generally deemed unsafe for the extreme loads placed on the stairway. The stringer length much be calculated—a relatively easy issue—and normally two or more long, solid, wide, pieces of wood are bought. Depending on the stair width and length, the expense of purchasing stringers is not great but is not insignificant. Then the stringers must be cut on site.
Each step is cut individually in triangular cuts removed from the stringers, and since the treads and risers of the staircase have thickness, the previous calculations of the height of each step are now adjusted to compensate in the cutting for the treads and risers which will be part of the step.
Obviously, numerous precise cuts on an expensive piece of wood are less than desirable for the builder. The possibility of a single cut passing entirely through the stringer and thus ruining it is present, as is the possibility of a single cut which is of proper depth but misplaced so badly that the wood cannot be recut correctly and with a safe strength, requiring the reinforcement or even replacement of the stringer.
Once the stringer is cut, the stairs risers and treads may finally be fastened to it.
The strength of the stringer is dramatically reduced by the cutting: after the expense and difficulty of using a 2×12 piece of wood as the stringer, that 2×12 may well have only a 2×6 thickness remaining at its narrowest and thus weakest points—where the stairs are cut the deepest into the stringers.
It is worth considering that pre-made stairs which might be nailed or otherwise fastened to an uncut stringer would only be usable in circumstances in which the height to be traversed measures EXACTLY a multiple of the stair height. For example, pre-made steps of exactly 8 inches each would be allowable for sets of stairs which cover a rise of exactly 16 inches, 24 inches, 32 inches and so on, but would NOT be allowable for stairs which need to cover a rise of 17 inches, 23 inches, 25 inches, and so on.
It would obviously be preferable to provide a device which allows the stringer to remain whole and uncut.
It would obviously be preferable to provide a device which allows the stringer to remain whole and uncut and thus stronger.
It would obviously be preferable to provide a device which allows the stringer to remain whole and uncut and thus allow the use of narrower and thus less expensive stringers.
It would obviously be preferable to provide a device which allows the builder to avoid the exasperating mathematics necessary to bridge a given rise and run with a set of equal stairs which meet all regulatory requirements.
These and many other issues are addressed by the present invention, whose advantages, aspects, objectives and embodiments are disclosed below.